HIGH-RESOLUTION RFLP MAP OF THE LONG ARM OF CHROMOSOME 5A IN WHEATS AND ITS SYNTENY AMONG CEREALS

A fine genetic map of the long arm of 5A in common wheat was generated by mapping 48 RFLP markers, in which 23 cDNAs were involved. That map was compared with the cytological map and a genetic map of the diploi d obtained from a cross between Triticum monococcum and T. boeoticum. The marker distribution of the genetic map of common wheat almost corr elated with the cytological distances, but some regions in which recom bination was suppressed were found; these were around the centromere a nd in the region adjacent to the central C-banding region (L1.5). Prom otion of recombination at the distal part of chromosome was not found. The marker order of the genetic map of common wheat was identical to that of the diploid, indicating that reciprocal translocation 4AL-5AL in wheat had taken place at the diploid level. Furthermore, this regio n was compared with the corresponding one of barley (5HL) and of rice (chromosome 9). Translocation was not detected in the barley chromosom e, but paracentric inversion was found in comparison with the correspo nding region of wheat. The translocation point in wheat seemed. to cor respond to the inversion point of barley, suggesting a hot-spot region for chromosome breakage. Strong suppression of recombination was foun d in the central part of 5HL. About two-thirds of the proximal region of wheat 5AL revealed synteny with the corresponding region of rice, w hereas there was no such relation in the more distal portion. Longer g enetic distances in the central part of 5AL, in comparison with the co rresponding region of rice, were found, indicating the presence of fac tors that affect recombination frequencies. The analyses suggest that the proximal part of chromosome arm 5AL has been relatively conserved, whereas the distal part has undergone more extensive rearrangements d uring evolution.